Abstract: On the basis of the second-order moment of the power density, the beam width, far-field divergence angle and M2 factor of nonparaxial cosine-squared Gaussian beams are illustrated and analyzed with numerical simulation。The conclusions are as following. (1) The waist width W0(0) increases with increasing w0/? parameter. W0(0) decreases with increasing decentred parameter ??when w0/? is relatively large (w0/?≥0.5). (2) As the parameter w0/?→0, the far-field divergence angle approaches an asymptotic value of ??max=63.4350, which is independent of the decentred parameter ?. (3) In the nonparaxial regime, the M2 factor of cosine-squared Gaussian beams depends not only on the decentred parameter ??? but also on the initial waist-width to wavelength ratio w0/?? The M2 factor may be less than 1 as w0/λbecomes small enough. The M2 factor does not always vary monotonically with w0/??for different decentred parameter ?? The M2 factor increases with increasing w0/??and reaches the maximum value, then gradually decreases, and finally tends to be a saturated value.

Key words: laser optics, nonparaxial cosine-squared Gaussian beam, power density, M2 factor